Method, system and optical network device for synchronizing time of a passive optical network

1. A method for synchronizing time in a Passive Optical Network (PON) comprising a master clock side and a slave clock side, the method comprising: receiving, at the slave clock side, a first PON protocol transmission frame carrying a first clock packet; acquiring, at the slave clock side, a first time at a first packet time stamp generating point located at a PON Media Access Control (MAC) layer of the first PON protocol transmission frame, the acquired first time being regarded as the time when the first clock packet is received; receiving, at the slave clock side, a second PON protocol transmission frame carrying a second clock packet, wherein the second clock packet carries the time when the first clock packet is sent; and adjusting, at the slave clock side, local time according to a difference between the time when the first clock packet is sent and the time when the first clock packet is received.

2. The method of claim 1 , wherein the first packet time stamp generating point is a certain bit of a Physical Synchronization (Psync) field in a frame header of a Gigabit PON Transmission Convergence layer (GTC) TC frame of the first PON protocol transmission frame at a GTC framing sub-layer.

3. The method of claim 1 , wherein the first packet time stamp generating point is located at a certain bit of a Header Error Control (HEC) field in a frame header of a Gigabit PON Encapsulation Method (GEM) frame of the first PON protocol transmission frame at a TC adapter sub-layer.

4. The method of claim 1 , further comprising: sending, at the slave clock side, a third PON protocol transmission frame carrying a third clock packet; acquiring, at the slave clock side, a second time at a second packet time stamp generating point located at the PON MAC layer of the third PON protocol transmission frame, the acquired second time being regarded as the time when the third clock packet is sent; receiving, at the slave clock side, a fourth PON protocol transmission frame carrying a fourth clock packet, wherein the fourth clock packet carries the time when the third clock packet is received; and correcting, at the slave clock side, the local time according to a difference between the time when the third clock packet is sent and the time when the third clock packet is received.

5. The method of claim 4 , wherein the second packet time stamp generating point is located at a certain bit of a Delimiter field in a frame header of a GTC TC frame of the third PON protocol transmission frame at the GTC framing sub-layer.

6. The method of claim 4 , wherein the second packet time stamp generating point is located at a certain bit of a HEC field in a frame header of a GEM frame of the third upstream frame at the TC adapter sub-layer.

7. The method of claim 4 , wherein the second packet time stamp generating point is located at a certain bit of a Physical Layer Overhead upstream (PLOu) field in a frame header of a GTC TC frame of the third PON protocol transmission frame at the GTC framing sub-layer.

8. The method of claim 7 , wherein: the first, second, third, and fourth clock packets are carried over an Ethernet protocol; or the first, second, third, and fourth clock packet are carried in IEEE 1588/1588v2 over GEM mode; each of the first, second, third, and fourth clock packet is carried in an Administration and Maintenance (OAM) message defined by PON protocol comprising at least one of a Physical Layer Operation, Administration and Maintenance (PLOAM) messages and an ONU Management and Control Interface (OMCI) message.

9. The method of claim 7 , wherein each of the first, second, third, and fourth clock packet is carried in IEEE 1588/1588v2 over GEM mode.

10. The method of claim 1 , further comprising: acquiring, at the master clock side, a third time at a third packet time stamp generating point located at the PON MAC layer of the first PON protocol transmission frame, the acquired time being regarded as the time when the first clock packet is sent; and sending, from the master clock side to the slave clock side, the second PON protocol transmission frame carrying the time when the first clock packet is sent.

11. The method of claim 10 , wherein the third packet time stamp generating point is located at a certain bit of a Physical Synchronization (Psync) field in a frame header of a Gigabit PON Transmission Convergence layer (GTC) TC frame of the first PON protocol transmission frame at a GTC framing sub-layer.

12. The method of claim 10 , wherein the third packet time stamp generating point is located at a certain bit of a Header Error Control (HEC) field in a frame header of a GPON Encapsulation Method (GEM) frame of the first PON protocol transmission frame at a TC adapter sub-layer.

13. An optical network device, comprising a processor configured to: receive a first PON protocol transmission frame carrying a first clock packet; acquire a first time at a first packet time stamp generating point located at a PON Media Access Control (MAC) layer of the first PON protocol transmission frame, the acquired first time being regarded as the time when the first clock packet is received; receive a second PON protocol transmission frame carrying a second clock packet, wherein the a second clock packet carries the time when the first clock packet is sent; and adjust local time according to a difference between the time when the first clock packet is sent and the time when the first clock packet is received.

14. The device of claim 13 , wherein the first packet time stamp generating point is a certain bit of a Physical Synchronization (Psync) field in a frame header of a Gigabit PON Transmission Convergence layer (GTC) TC frame of the first PON protocol transmission frame at a GTC framing sub-layer.

15. The device of claim 13 , wherein the first packet time stamp generating point is located at a certain bit of a Header Error Control (HEC) field in a frame header of a Gigabit PON Encapsulation Method (GEM) frame of the first PON protocol transmission frame at a TC adapter sub-layer.

16. The device of claim 13 , the processor further configured to: send a third PON protocol transmission frame carrying a third clock packet; acquire a second time at a second packet time stamp generating point located at the PON MAC layer of the third PON protocol transmission frame, the acquired second time being regarded as the time when the third clock packet is sent; receive a fourth PON protocol transmission frame carrying a fourth clock packet, wherein the fourth clock packet carries the time when the third clock packet is received; and correct the local time according to a difference between the time when the third clock packet is sent and the time when the third clock packet is received.

17. The device of claim 16 , wherein the second packet time stamp generating point is located at a certain bit of a Delimiter field in a frame header of a GTC TC frame of the third PON protocol transmission frame at the GTC framing sub-layer.

18. The device of claim 16 , wherein the second packet time stamp generating point is located at a certain bit of a HEC field in a frame header of a GEM frame of the third upstream frame at the TC adapter sub-layer.

19. The device of claim 16 , wherein the second packet time stamp generating point is located at a certain bit of a Physical Layer Overhead upstream (PLOu) field in a frame header of a GTC TC frame of the third PON protocol transmission frame at the GTC framing sub-layer.

20. A point-to-multipoint optical communications system, comprising an Optical Line Termination (OLT) and an Optical Network Unit (ONU), wherein: the OLT comprises: means for forming a downstream Passive Optical Network (PON) protocol transmission frame from the OLT to the ONU and processing an upstream PON protocol transmission frame from the ONU to the OLT; a master clock synchronization processing module, configured to send a first clock packet carried in a first downstream PON protocol transmission frame and a second clock packet carried in a second downstream PON protocol transmission frame to the ONU, wherein the second clock packet carries the time when the first clock packet is sent; and a master clock packet time stamp generating module, configured to acquire time according to frame data of the first clock packet at a PON Media Access Control (MAC) layer and regard the acquired time as the time when the first clock packet is sent; the ONU comprises: means for forming a upstream PON protocol transmission frame upstream PON protocol transmission frame from the ONU to the OLT and processing a downstream PON protocol transmission frame from the OLT to the ONU; a slave clock packet time stamp generating module, configured to acquire time according to frame data of the first clock packet at the PON MAC layer and regard the acquired time as the time when the first clock packet is received; and a slave clock synchronization processing module, configured to receive the first downstream PON protocol transmission frame and the second downstream PON protocol transmission frame and adjust local time of the ONU according to a difference between the time when the first clock packet is sent and the time when the first clock packet is received.